For patients with high-risk neuroblastoma (NB) survival remains below 40%, and survivors suffer from life-long treatment-related disabilities. This necessitates the development of new targeted therapies. Small-molecule inhibitors of insulin-like growth factor 1 receptor (IGF1R) exhibit antitumor effects on NB cells in vitro and in vivo. Yet given the apparent lack of somatic mutations in the IGF1R gene, it remains to be determined what subset of NB patients would benefit from this approach. We hypothesized that IGF1R expression is controlled by alterations in the 3'UTR which would affect binding by microRNAs. In our Preliminary Experiments, we first focused on the genetic variant rs3833015, which is a small 2-nt deletion found in ~50% of NB patients. The positive effects of this 3'UTR variant on IGF1R expression were established using luciferase sensor essays, immunoblotting of commonly available NB cell lines, and transcriptome profiling of 28 primary neuroblastomas using Gene Set Enrichment Analysis. Furthermore, rs3833015-overexpressed genes were also strongly enrichment for members of the IGF1R/MAPK pathway, which plays a well-established role not only in cell proliferation but also in cell survival in the face of chemotherapy. In paralel, during the course of unbiased expression-quantitative trait loci (eQTL) studies, we identified another variant, rs3743251, which creates a new miR-binding site and correlates with decreased IGF1R mRNA levels. Our current overall hypothesis is that rs3833015 and rs374251 change IGF1 signaling (up and down, respectively), resulting in altered resistance to conventional chemotherapeutic agents and small-molecule IGF1R inhibitors. We will pursue this hypothesis in the following two Aims. 1. To determine the mechanisms of IGF1R deregulation by rs3833015 and rs3743251 and to identify new SNPs linked to IGF1R over/under-expression. 2. To investigate the contribution of IGF1R variants to neuroblastoma sensitivity to small-molecule IGF1R inhibitors and chemotherapeutic agents. To this end, we will correlate IGF1R 3'UTR genotypes with survival of NB patients using Kaplan-Meier analysis and compare and contrast responses of rs3833015 and rs374251 tumors to conventional therapeutics (cyclophosphamide and topotecan) and IGF1R inhibitors. The main impact of this study is that it would allow prospective stratification of patients enrolled in clinical trials of IGF1R inhibitors nd more robust responses to these drugs, ushering in the era of miR pharmacogenomics.